1. Field of the Invention
The present invention relates to image reading devices for reading a first side and a second side of an original using different reading units and reading-characteristic correction methods for the image reading devices.
2. Description of the Related Art
An image reading device provided in a copying machine and configured to, in order to improve productivity, read the front and back sides of an original using a front-side reading unit and a back-side reading unit without inverting the original front-to-back is known (see, for example, Japanese Patent Laid-Open No. 2004-187144).
Such an image reading device reads the front and back sides of an original using different reading units. Thus, in a case where portions having the same image density are read using the front-side reading unit and the back-side reading unit, a difference in reading level may occur between the front-side reading unit and the back-side reading unit. In such a case, reproduced color and density may be different between the front side and the back side of the original.
A method for performing image correction such that the density of image data read by a front-side reading unit and the density of image data read by a back-side reading unit are matched by using a unit configured to correct a difference in reading level between the front-side reading unit and the back-side reading unit is available (see, for example, Japanese Patent Laid-Open No. 2005-210268).
In addition, a method for reading an adjustment original using a first reading unit and a second reading unit and determining gamma correction tables and color correction factors such that values of color components read by the first reading unit and values of the corresponding color components read by the second reading unit are matched is available (see, for example, Japanese Patent Laid-Open No. 2006-229466).
In the method described in Japanese Patent Laid-Open No. 2005-210268, in the case of a monochrome image, the image densities of the front and back sides are matched. However, in the case of a color image, correction of a difference in image color between the front and back sides cannot be sufficiently performed in this method. That is, even if the image densities of the front and back sides can be matched in the case of a monochrome image, color tones of the front and back sides may not be the same in the case of a color image. In particular, a difference in color tone between a low-brightness portion on the front side and a low-brightness portion on the back side tends to be noticeable.
In the method described in Japanese Patent Laid-Open No. 2006-229466, the color tone of a portion read by the first reading unit and the color tone of a portion read by the second reading unit can be matched. However, since a memory for generating gamma correction tables is necessary, the circuit scale is increased and the cost is also increased.